Since milling generally employs a plurality of cutting inserts mounted on the lateral surface of a milling cutter for machining a workpiece, the cutting capability is markedly varied depending on the cutting depth and the shape of inserts.
Conventionally, deep grooves or surfaces were machined using a milling cutter with a plurality of square plate type cutting inserts mounted on its lateral surface. However, inserts of this shape cause a high cutting resistance, and is uneconomical due to fewer numbers of available cutting edges. In cases where a plurality of inserts is used, machining quality is deteriorated due to discontinuities in insert profile. Since a plurality of inserts is mounted in axial direction as well as in circumferential direction, inserts are mounted with cutting edges in an overlapped fashion in order not to leave unmachined portions in axial direction. Here, machined surface might have scratches over the overlapped portions by sharp edge corners. If corners of the cutting edges are damaged, the neighboring cutting edges are also damaged, and then the service life of the insert is shortened.